Mixed oxide nuclear fuel pellets are typically sintered in a reducing atmosphere in a sintering furnace with a maximum of 6% hydrogen for safety reasons. Negative pressure glove boxes are used to prevent the escape of plutonium into the worker environment. There has been recent renewed interest in the fabrication technology for mixed oxide nuclear fuel pellets and, hence, renewed interest in the sintering operation which comprises the critical processing step in the fabrication of such pellets. Sintering establishes both the physical and chemical properties of the nuclear fuel necessary for reactor irradiation. Because the sintering operation is the controlling or limiting process in the fabrication of such pellets, a failure in that operation results either in the reduction or termination of fuel production until repair or replacement of the sintering furnace can be accomplished.
Continuous sintering furnaces utilized during the fabrication of nuclear fuel pellets, particularly urania fuel, are large and massive. Practically, the large size of these furnaces precludes their use in a glove box arrangement required for MOX fuel pellet fabrication because of the difficulty associated with operation and maintenance. Glove boxes tend to be dimensionally small, although operating height is normally controlled by the size of the contained equipment. Because limited access techniques, e.g., glove ports, lead to operating and maintenance times which result in substantial downtimes in the pellet fabrication process, either the furnace capacity must be duplicated or easily maintainable furnace designs must be utilized. Duplication of furnaces to provide reliable production capacity is both very expensive and space-intensive. Small batch furnaces are readily maintainable but the production capacities are low and product uniformity is inconsistent.
Previously, MOX fuel pellets have been sintered in either small batch furnaces or reduced in size continuous furnaces designed for urania fabrication. The capacity of the batch furnaces is limited by the physical size associated with critically safe quantities of the nuclear material. Additionally, process variability has been observed between different sintering cycles and between different furnaces, which results in a final sintered product with variable uniformity. While large continuous sintering furnaces tend to eliminate the pellet uniformity problems, the difficulties associated with operating and maintenance cycles result in increased process downtime.